Meiosis in Cicer L. Species : The Relationship between Chiasma Frequency and Genome Length

抄録

Meiotic chromosome pairing configurations were studied in 24 accessions representing all of the 9 annual Cicer species. The diploid chromosome number was confirmed to be 2n=16 in all the studied species. Meiosis in Cicer species was characterized by a rather diffused prophase, but nonetheless it progressed normally. Precocious as well as late disjunction of the longest chromosome pair was occasionally observed giving rise to false univalents and anaphase bridge, respectively. Regular 8 bivalents were characteristically observed in all the species. Only one chromosome pair was found to be associated with the nucleous at pachynema and/or diakinesis stage in all the accessions and species, including C. reticulatum which has been reported to have 2 pairs of satellited chromosomes containing rRNA gene cluster. There was little variaiton in chiasma frequency per PMC among accessions within a species, but considerable variation among species. The mean number of rod bivalents per PMC ranged from 2.62 in C. cuneatum to 6.12 in C. echinospermum, while the number of ring bivalents per PMC ranged from 1.89 in C. echinospermum to 5.38 in C. cuneatum. Chiasma frequency per unit genome length was primarily a function of the diploid genome length and showed a negative relationship (Y =0.780-0.016X, r² = 0.86). The role of proportion of repetitive DNA sequences, in the form of heterochromatin, present in the genome and its distribution among chromosomes of the various Cicer species genome have been speculated to explain this negative relationship.